DE 3149412 A1 describes a circuit arrangement for establishing connections that are free of charge for the calling party to pre-specified subscriber lines in a telephone call processing system. The directory number of the assigned subscriber line is determined by dialing a special service number then suffix-dialing a number designating pre-specified subscriber lines. When the connection has been successfully switched through, call-charge logging takes place in each case to the account of the pre-specified other subscriber line. Dialing the special service number serves to access a private automatic branch exchange connected to the relevant local exchange. This private automatic branch exchange also performs the functions of determining the directory number and of establishing the remainder of the connection to the pre-specified other subscriber line. With the aid of announcement equipment, attendant consoles, and subscriber lines connected to the private automatic branch exchange, the calling party receives appropriate support that may comprise the conveying of announcement texts, the provision of information, or entering of the directory number at the attendant console.
NL1013397 C2 proposes that an owner of a telephone number selects other telephone numbers and authorizes these to call the owner's directory number at the owner's expense. These numbers are supported by the operator of the network via which the owner of a telephone number is connected.
There are situations in which a communication network subscriber would like to conduct a call with other subscribers at their expense when. For example, when a pre-paid account of a mobile station or SIM card is exhausted or when company employees are willing to be accessible for business purposes on their private mobile station, but are not prepared to call their company at their own expense. Operators of fixed networks offer collect calls (telephone calls the connection costs of which are charged to the called line). The use of collect calls is very tedious and expensive for both parties. Operators incur high personnel costs as the result of providing a service of this type because this type of service is at present only switched by an attendant (manual switching). Mobile network operators do not offer this service owing to the high personnel costs thereby incurred.
Another solution would be for the calling party to send an SMS message to another party to the effect that the calling party wishes to be called back. Charges will still be due even though the SMS message costs little. As no more SMS messages can be sent if a pre-paid account is exhausted, this solution will not work in that case. The same applies if the calling party only calls another party for a very brief period and requests a callback.